1. Field of the Invention
The present invention relates to a roll of laminate for capacitor layer for withstand voltage inspection and a method of measuring withstand voltage using this roll of laminate for capacitor layer for withstand voltage inspection.
2. Description of the Related Art
A laminate in which electrically conductive layers are disposed on both sides and a dielectric layer is provided between the electrically conductive layers like a laminate related to the present invention has thitherto been widely used as a basic material for forming a capacitor layer, mainly, of a printed wiring board. This material for forming a capacitor layer is what is called a double-sided clad laminate and has been manufactured by disposing copper laminate on both sides of a dielectric layer component material, such as a prepreg in which a semicuring resin constituting a dielectric layer is impregnated in glass cloth etc. and a semicuring resin sheet, and hot pressing the copper laminate.
In such a manufacturing method as described above, a manufacturing method of a copper clad laminate used in the fabrication of conventional printed wiring boards is used as it is, and it has been general practice to adopt a manufacturing method which, for example, involves disposing a plurality of daylights between a set of hot press plates for press forming, laminating metal foil and a dielectric layer component material between the daylights so as to form a plurality of double-sided laminates, superposing these materials in multiple layers, and bonding these materials together by hot pressing. During this press working, pressing conditions are set so that the semicuring resin of the dielectric layer component material starts reflow and flows out over a fixed distance from an end of the laminate. This is necessary from the viewpoint of promoting the action of an air vent present between an aggregate material such as a glass cloth and an impregnated resin, improving the wettability between the bonded surface of the metal foil and the resin and increasing the bonding strength between the metal foil and the dielectric layer.
Under such a method as described above, a schematic view as shown in FIG. 10(A) is obtained when a section of a double-sided laminate immediately after hot press working is observed. Ends of this double-sided clad laminate 10 are cut by a shearing cutter etc. after that and a double-sided copper laminate as a product is completed.
However, if end treatment as described above is performed for a double-sided clad laminate having a thin dielectric layer as used in the formation of a capacity layer, it follows that the phenomenon described very schematically below by referring to drawings occurs. The double-sided clad laminate in the state obtained by press working is shown in FIG. 10(A). When the end portions of this double-sided clad laminate are cut from up to down by means of edges 11 of a shearing cutter, particularly in a case where the metal material is a soft material, such as copper, this phenomenon is remarkable. That is, top side metal foil 12 is elongated and stretched toward bottom side metal foil 13 in association with the movement of the edges 11 of the shearing cutter and the leading end portions of the top side metal foil 12 come into contact with the bottom side metal foil 13. This is the state shown in FIG. 10(B).
In such a state, the electrically conductive layers on both sides form short circuits, with the result that even when the interlayer withstand voltage of a double-sided clad laminate used in the formation of a capacity layer is to be measured, the measurement becomes impossible in this state. Therefore, it becomes impossible for clad laminate makers to perform complete quality assurance because they cannot check interlayer resistance as a double-sided clad laminate for the formation of a capacity layer.
It is also possible to conceive that if such a state as shown in FIG. 10(B) is generated, the end portions of a double-sided clad laminate after the cutting thereof by use of a shearing cutter are polished by polishing means, such as a grinder, to produce good end surfaces. However, in the case of a double-sided laminate used for the formation of a capacity layer, a problem as described below arises even when good end surfaces are produced.
That is, a thin dielectric layer is common to double-sided clad laminates used for the formation of a capacity layer. Particularly in recent years, even double-sided clad laminates having a dielectric layer which is as thin as 20 μm or so have been manufactured. When a double-sided clad laminate has such a thin dielectric layer 4 and electrically conductive layers of metal foil 12, 13 are present up to the end portions of the laminate, the discharge phenomenon occurs at the edge portions of the electrically conductive layer on both sides between the end portions of the laminate, which are indicated by an arrow m FIG. 11, and it becomes almost impossible to accurately measure withstand voltage. In particular, the interlayer withstand voltage test of a double-sided clad laminate used for the formation of a capacity layer is conducted by applying a high voltage of not less than 500 V and hence the discharge phenomenon in the electrically conductive layers at the end portions of the laminate is apt to occur.
In order to solve such a problem as described above, the present inventors provided, in Patent Literature 1 (Japanese Patent Application No. 2002-157067), a double-sided clad laminate which enables the interlayer withstand voltage of a double-sided clad laminate used in the formation of a capacity layer to be measured in a simpler manner in the state of the double-sided clad laminate and which can supply a quality assured product and a method of manufacturing this double-sided clad laminate.
The invention disclosed by the present inventors in Patent Literature 1 is based on the use of “a double-sided copper clad laminate for the formation of a capacity layer in which copper foil is clad to both sides of a dielectric layer, wherein the copper foil shape on both sides of the double-sided copper clad laminate is in an analogous relation, with the size of first copper foil on one side being smaller than that of second copper foil on the other side, the first copper foil and the second copper foil being disposed concentrically via the dielectric layer, and wherein a peripheral portion of an edge end of the side of the double-sided copper clad laminate to which the first copper foil is clad has a dielectric region in which the dielectric layer is exposed,” and withstand voltage inspection is performed for each lamination of what is called a double-sided copper clad laminate.
However, a laminate for capacitor layer related to the present invention is a laminate web for capacitor layer fabricated by sequentially laminating a first electrically conductive layer formed from a metal foil laminate, a dielectric layer and a second electrically conductive layer formed from a metal foil web and bonding the these layers in a laminated state into one piece. In fabricating this laminate web for capacitor layer, it is possible to adopt several continuous laminating methods, such as a method by which continuous laminate forming is performed using two metal foil webs and a film material constituting a dielectric layer, and a method by which continuous laminate forming is performed, with the dielectric layer sides of two dielectric-layer-formed metal foil webs opposed to each other.
It is a laminate web for capacitor layer that is obtained by a continuous laminating method in this manner. Winding this laminate web for capacitor layer around a core tube in a rolled state is desirable from the standpoint of raising the production efficiency and besides this is also desirable in terms of safety during product transportation and less storage space.
When a laminate web for capacitor layer manufactured by this continuous laminating method is used, it is used after being cut to an arbitrary size. Therefore, in this laminate web for capacitor layer which has been cut, various problems as shown in FIG. 10(B) arise and the application of the invention disclosed in Patent Literature 1 becomes difficult.
In the continuous laminating method, techniques which permit withstand voltage measurement in a rolled state have been desired in order to supply to the market products in which the production efficiency of laminates for capacitor layer is high and which are more inexpensive.